Fog reduction in photographic silver halide emulsions



United States Patent 3,244,522 FOG REDUCTION IN PHOTOGRAPHIC SILVERHALIDE EMULSIONS Robert J. Clementi, Fritz Dersch, and Sally L. Dwyer,Binghamton, N.Y., assignors to General Aniline & Film Corporation, NewYork, N.Y., a corporation of Dela ware N0 Drawing. Filed Sept. 26, 1962,Ser. N0. 226,474 8 Claims. cl. 96-66) The present invention relates tophotographic elements containing a light-sensitive silver halideemulsion and to the use in intimate contact with such emulsions ofcompounds which serve as anti-fogging and stabilizing agents therefor.

It is known that light-sensitive silver halide emulsions have a tendencyto log. Fog is caused in a number of ways, e.g., by prolonged ripeningof the emulsions during storage of the film or paper, particularly atelevated temperature and humidity, or by the use of chemicalsensitizers, particularly alkylene oxide derivatives, as described inUnited States Patents 2,704,716, 2,716,062 and 2,728,666. Prolongeddeveloping time may also cause fogging.

A great number of anti-foggants and stabilizers have been described inthe literature as being effective in preventing an increase in fogthereby stabilizing or controlling the keeping-quality of thelight-sensitive silver halide emulsions.

Mees in The Theory of the Photographic Process," published by theMacMillan Company, New York, 1946, discusses the use of anti-foggants onpages 459 et seq. Although many of these compounds have the ability toreduce fog tendencies, they have shortcomings in most cases in that theylower the sensitiviey of the emulsions and in many instances reduce theoptical or dye sensitization.

An object of our invention is to provide stabilizers or fog inhibitingagents which tend to prevent the formation of chemical fog inlightsensitive silver halides.

A further object is to provide stabilizers or anti-fogging agents forlight-sensitive silver halide emulsions which do not appreciably lowerthe sensitivity of the emulsions.

A still further object is to provide stabilizers or antifogging agentsfor light-sensitive silver halide emulsions which do not reduce thesensitivity to light of longer wave lengths eifected by the presence ofsensitizing dyes.

Other objects and advantages will appear from the specification.

It has been discovered that a very effective class of stabilizers oranti-fogging agents for light-sensitive silver halide emulsions arethose having the following general formula:

wherein R is methyl, ethyl, methyl mercapto or ethyl mercapto and R ismethylene or ethylene, the alkylene value for R always being the same asthe alkylene value for R and the R'SH group being in a position 0-, morpto the R group.

Examples of compounds contemplated by the above general formula are:

(l) a,a-Dimer capt o-p-xylene of the formula CHaSH onisna,a'-Dimercapto-m-xylene.

a,a-Dimercapto-o-xylene.

a-Mercapto-p-xylene of the formula 0 H1811 a-Mercapto-m-xylene.-Mercapto-o-xylene.

HaCHz SH (8) @B -Dimercapto-m-diethyl benzene. (9) 5,3-Dimercapto-o-diethyl benzene. (10) fi-Mercapto-p-diethyl benzene ofthe formula CHZCIH3 (l l fi-Mercapto-m-diethyl benzene. (12)fl-Mercapto-o-diethyl benzene.

residue diluted with water and extractedwith ether.

The ether is evaporated to leave an" oil which is treated with dilutedsodium hydroxide. The alkaline solution is filtered to remove unwantedproducts, the filtrate acidified with dilute sulfuric acid and themercaptan extracted with ether. The ether is evaporated and the oilyproducts distilled under vacuum.

a,a-dimercapto-o-xyl ene is prepared in the same manner excepting thato-xylene bromide is substituted for the p-xylene bromide.

B, 3'-Dimercapto-p-diethyl benzene of the formulaa,a-dimercapto-m-xylene is also prepared in the same way but while usingm-xylene bromide in lieu of p-xylene bromide.

The a-mercapto xylenes are also prepared in a similar fashion but byusing one equivalent of KSH rather than two, as in the preparationspreviously described.

The diethyl benzene derivatives are prepared in a like manner exceptingthat the xylene bromide is replaced by diethyl benzene. If dimercaptoderivatives of the diethyl benzene are desired two equivalents of KSHare used per one equivalent of diethyl benzene bromide. If themonomercapto derivative is desired, then equal molar quantities of KSHand diethyl benzene bromide are employed.

Beneficial effects in fog reduction may be obtained with solutions ofthe above compounds incorporated in the silver halide emulsions asripening finals or as coating finals. Ripening finals are added duringthe ripening or the sensitivity stage of the emulsion making process.Such additions may be effected before, during or after the addition of asoluble silver salt to the soluble halide in the presence of a solublephotographic colloid, such as gelatin, PVA, PVP, solubilized casein oralbumin.

Coating finals are added to the emulsion just prior to coating it on asuitable support, i.e., glass, paper or film when the emulsion hasnearly obtained its maximum sensitivity.

When used as ripening finals our anti-foggants or stabilizers are bestused in a concentration of .02 to milligrams per .6 mole of silverhalide and when used as coating finals in a concentration of 1 to 20milligrams per .6 mole of silver halide. In many emulsions we prefer toapply our anti-foggants or stabilizers in a gelatin surface coating formaximum effectiveness. The concentration used depends very much on thetype of emulsion employed and it is advisable to determine the optimumconcentration from case to case.

The anti-foggants and stabilizers may be employed in various types ofphotographic emulsions, e.g., non-sensitized, orthochromatic,panchromatic, X-ray emulsions, paper emulsions and color emulsions. Theymay be used in combination with other known anti-foggants or stabilizersor in combination with sulfur-, reductionmetal-and noble metalsensitizers, or in combination with polyoxyalkylenes and theirderivatives.

Equally good results are obtained in the event that the anti-foggants orstabilizers are used in one or all processing baths or in preandpost-baths, particularly in the photographic developer.

The invention is further illustrated by the following examples which areexemplary and not limitative:

Example I A silver halide emulsion in gelatin containing 2% silveriodide and 98% silver bromide was prepared in a conventional manner andbrought up to its maximum light sensitivity. It was then readied forcoating and finals were added such as sensitizing dyes and hardeningagents. A 0.01% solution of a,a-dimercapto para-xylene was added to theemulsion as an anti-foggant and stabilizer. The emulsion samplescontained about 0.6 mole of silver halide. The so prepared emulsionsamples were coated on a cellulose ester base and dried. Samples ofthese film coatings were then exposed in a Type 18 sensitometer anddeveloped in a developer of the following composition:

Grams Metol 1.5 Sodium sulfite, anhydrous 45 Sodium bisulfite 1Hydroquinone 3 Sodium carbonate, monohydrate 6 Potassium bromide 0.8

Water to make 1 liter.

Quantity of Compound Relative Fog at 12 Oven Fog at Used Speed Dev. 6Dev.

Example 11 The procedure is the same as in Example I excepting thatthere is added fifl-dimercapto-p-dietliyl benzene in lieu of thep-xylene derivative. The results are substantially the same.

Example III Exposed samples of a photographic film were developed fortwelve minutes at 65 F. in a standard metol-hydroquinone developer. Twotests were made, one with a developer containing 4 mg. ofa,a'-dimercapto para-xylene per one liter of developer. Sensitometricstrips, developed in the normal developer (control) for twelve minutesshowed a fog of .30, whereas those strips, which were developed in thedeveloper containing the antifoggant, had a fog of .18.

Example IV A silver halide emulsion in gelatin containing 2% silveriodide and 98% silver bromide was coated on film base in a manner knownto the art. After the coating, an aqueous gelatin solution containing 20grams of gelatin in 1 liter of H 0 and 8 mg. of e,a-dimercaptopara-xylene Was coated thereon as an antiabrasion layer. After drying,film samples were exposed and processed as described in Example I. Thesamples exhibited a relative speed of 100 and a fog of .18 compared withtype coating of the above emulsion having an antiabrasion layer similarto that described above, but lacking the antifoggant and having a speedof 100 and a fog of .30.

Example V The procedure is the same as in Example I except that thep-xylene derivative thereof is replaced by an equivalent quantity ofa-mercapto-p-xylene. sults are obtained.

Example VI RSH wherein R is selected from the class consisting ofmethyl, ethyl, methyl mercapto, and ethyl mercapto and R is selectedfrom the class consisting of methylene and ethylene, the alkylene valuefor R always being the same as the alkylene value for R and the RSHgroup being in a position selected from the class consisting of the o-,111- and p-positions to the R group.

2. The product as defined in claim 1 wherein the compound is located inthe silver halide emulsion.

Equivalent re- 3. The product as defined in claim 1 wherein the compoundis located in an antiabrasion overcoating for the silver halideemulsion.

4. The product as defined in claim 1 wherein the compound isa,a-dimercapto-p-xylene.

5. The product as defined in claim 1 wherein the compound isa-mercapto-p-Xylene.

6. The product as defined in claim 1 wherein the compound is,8,,8'-dimercaptop diethyl benzene.

7. A process of reducing the tendency of an exposed photographic silverhalide emulsion to fog on development which comprises developing saidemulsion with a developer containing a compound of the followingformula:

wherein R is selected from the class consisting of methyl, ethyl, methylmercapto and ethyl mercapto and R is selected from the class consistingof methylene and ethylene, the alkylene value for R always being thesame as the alkylene value for R and the RSH group being in a positionselected from the class consisting of the 0-, mand p-positions to the Rgroup.

8. A process of reducing the tendency of a photographic silver halideemulsion to fog on development which comprises exposing the emulsion anddeveloping it in a metol-hydroquinone developer containing a smallamount of a,ot-dimercapto-p-xylene.

References Cited by the Examiner UNITED STATES PATENTS 2,956,876 10/1960Spath 9666 3,008,829 11/1961 Clementi et al 96109 NORMAN G. TORCHIN,Primary Examiner.

J. T. BROWN, Assistant Examiner.

7. A PROCESS OF REDUCING THE TENDENCY OF AN EXPOSED PHOTOGRAPHIC SILVERHALIDE EMULSION TO FOG ON DEVELOPMENT WHICH COMPRISES DEVELOPING SAIDEMULSION WITH A DEVELOPER CONTAINING A COMPOUND OF THE FOLLOWINGFORMULA: